Unix is a powerful, multi-user environment that has been implemented on a variety of platforms. Once the domain of servers and advanced users, it has become accessible to novices as well through the popularity of Linux and Mac OS X. With the notable exception of Microsoft Windows, all current major operating systems have some kind of Unix at their cores.

Unix was developed at Bell Labs in 1969, but in the past three decades many others have contributed to its evolution. In reality, Unix is not so much a single operating system as it is a standard upon which organizations and companies base their own systems. Examples of Unix implementations include Mac OS X/Darwin (Apple), GNU/Linux, AIX (IBM), Solaris (Sun), IRIX (SGI), and FreeBSD. They have different graphical interfaces, but from the Unix shell, a command line feature common to all versions, they are very similar.

Most of the UITS shared central systems at Indiana University are Unix servers and workstations, including Big Red (research; no email) and Quarry (general use, research; no email).

As with other operating systems, there are many kinds of applications available on a Unix system. Email, newsreading, programming, statistics, and graphics are some of the areas for which Unix software exists. Unix was once distinct from other operating systems because of its high level of integration with the network and its multi-user environment. Each user who logs in can have an environment distinct from that of any other user. In recent years, however, this distinction has blurred as other operating systems have developed these capacities. With the introduction of Mac OS X and the increasing popularity of free Unix systems like Linux and FreeBSD, as well as advanced interfaces based on the X Window System, more individuals are also using Unix as the operating system for their personal workstations.